This invention relates to certain tris(dialkylamino)sulfonium compounds having utility as polymerization catalysts, and to processes for preparing these compounds.
Middleton, U.S. Pat. No. 3,940,402, discloses a class of tris(dialkylamino)sulfonium salts of the general formula ##STR1##
In the foregoing formula, the R groups are alkyl groups having 1 to 20 carbon atoms, each alkyl having at least two alpha hydrogen atoms, and X can be (CH.sub.3).sub.3 SiF.sub.2, Cl, Br, I, CN, NCO, NCS, NO.sub.2 or N.sub.3. This patent also discloses a method for preparing difluorotrimethylsilicate salts of the formula (R.sup.1 R.sup.2 N)(R.sup.3 R.sup.4 N)(R.sup.5 R.sup.6 N)S.sup.+ (CH.sub.3).sub.3 SiF.sub.2.sup.-, by reacting sulfur tetrafluoride (SF.sub.4) with at least 3 mole equivalents of a selected dialkylaminotrimethylsilane. The patent further discloses a method for preparing a sulfonium chloride salt in which X is Cl, by reacting the aforementioned difluorotrimethylsilicate salts with a suitable chlorine-releasing compound, e.g. .alpha.-chlorotoluene. Finally, the patent describes a process for preparing the remaining salts by reacticn of the sulfonium chloride with appropriate reagents, e.g., sodium bromide, sodium cyanide, sodium thiocyanate, sodium nitrite, sodium azide or sodium cyanate.
Durrant et al., Introduction to Advanced Inorganic Chemistry, John Wiley & Sons, Inc., New York, pp 926-927 (1970) disclose processes for preparation of bifluorides of ammonium, alkylammonium, and alkali metal compounds by partial neutralization of a solution of hydrofluoric acid (HF) with a metal hydroxide or ammonium hydroxide. According to this reference, alkali metal fluorides absorb HF to form bifluorides, i.e. KF+HF.fwdarw.KHF.sub.2. In addition, Durrant et al. disclose that ammonium fluoride (NH.sub.4 F) can be converted to ammonium bifluoride by heating, i.e. 2NH.sub.4 F.fwdarw.NH.sub.4 HF.sub.2 +NH.sub.3.
However, House, et al., Thermochimica Acta 47:213-216 (1981) describe studies of thermal decomposition of ammonium fluoride, and conclude that "no evidence" could be found to support the existence of the reaction 2NH.sub.4 F.fwdarw.NH.sub.4 HF.sub.2 +NH.sub.3.
Fujiwara, et al., J. Am. Chem. Soc. 96:7625 (1974) disclose a process for thermally decomposing tetraethylammonium fluoride to provide tetraethylammonium bifluoride and other products. Deuterium-containing tetraethylammonium bifluoride was prepared by dissolving the bifluoride in deuterium-enriched water and evaporating excess water.
Delyagina et al., Isvest. Akad. Nauk. SSSR, Ser. Khim., 10:2238 (1981), Eng. trans., disclose an ionic bifluoride [(CH.sub.3).sub.2 N].sub.2 CH.sup..sym. HF.sub.2.sup..crclbar., prepared by reacting difluoromethylamine with dimethylamine in dimethylformamide.
Bifluoride salts, e.g., alkali metal bifluorides or ammonium bifluorides, are known to be useful catalysts in certain reactions, including certain polymerization reactions. Tuller, et al., U.S. Pat. No. 4,074,036, disclose a process for preparing polyanhydrides by copolymerization of a maleic monomer and selected alkyl-substituted styrenes in the presence of an alkali metal bifluoride catalyst.